The invention relates to a method of extruding material, in which method the material is extruded with an apparatus comprising at least one rotor and at least one stator, the rotor and stator comprising grooves, whereby the grooves make the material move through the apparatus when the rotor is rotated.
The invention further relates to an apparatus for extruding material, the apparatus comprising at least one rotatable rotor and at least one stator, the rotor and the stator comprising grooves, whereby the grooves make the material move through the apparatus when the rotor is rotated.
WO 97/21532 discloses an apparatus comprising a conical rotor arranged between two stators. Helical grooves are arranged in the rotor and/or the stator for extruding the extrudable material from the extruder as the rotor rotates. Furthermore, the rotor is provided with an opening or openings via which at least part of the extrudable material is arranged to flow. The publication also presents a solution in which the rotor and the stator are provided with grooves, which serve to mix the extrudable material. The apparatus homogenizes and mixes the extrudable material. However, the apparatus does not always melt the material sufficiently efficiently. Furthermore, the apparatus is quite ineffective in treating waste material.
WO 99/11374 discloses a method and an apparatus for treating waste material. The apparatus comprises a conical rotatable rotor arranged between stators. The stators are provided with grooves that serve to discharge the material from the apparatus as the rotor 3 rotates. The rotor is provided with openings through which the material is arranged to pass. The edges of the openings and grooves are sharp, so that when the waste material fed into the apparatus passes through the openings, the sharp edges grind it. This apparatus is extremely efficient in treating waste material. However, the apparatus is quite complex, and the travel and management of the material flows require exact dimensioning and an experienced user.
It is an object of the present invention to provide a method and an apparatus for efficiently melting and treating the treatable material.
The method of the invention is characterized in that the rotor and stator surfaces facing each other have a wavelike cross-section, and the rotor and stator grooves are so arranged that at the ridge of a wave the depth of a groove reaches its maximum, and at the bottom of a wave the depth of a groove reaches its minimum, and the bottom of the wave in the rotor is at the ridge of the wave in the stator and vice versa, whereby the material moves alternately from a rotor groove to a stator groove, and back.
The apparatus of the invention is characterized in that the rotor and stator surfaces facing each other have a wavelike cross-section, and the rotor and stator grooves are so arranged that at the ridge of a wave the groove reaches its maximum depth, and at the bottom of a wave the groove reaches its minimum depth, and the bottom of the wave in the rotor is at the ridge of the wave in the stator and vice versa, whereby the material is arranged to move alternately from a rotor groove to a stator groove, and back.
The essential idea of the invention is that the rotor and stator surfaces facing each other have a wavelike cross-section, and the rotor and stator are provided with grooves in such a way that at the ridge of a wave the depth of a groove reaches its maximum, and at the bottom of a wave the depth of a groove reaches its minimum. Further, the bottom of the wave in the rotor is at the ridge of the wave in the stator and vice versa, whereby the material is arranged to move alternately from a rotor groove to a stator groove, and back. The wavelike surface between a rotor and a stator makes the material get sheared when it moves from a rotor groove to a stator groove and from a stator groove to a rotor groove. The apparatus has an extremely good melting and mixing efficiency and it can also be used to efficiently treat waste plastic and non-meltable or poorly meltable material. The yield of the apparatus is also very good. It is the idea of a preferred embodiment that the cross-section of the rotor and stator surfaces facing each other is saw-tooth wavelike, whereby the entire apparatus is easy to make by machining, for example. It is the idea of a second preferred embodiment that the pitch angles of the rotor and stator grooves are so arranged that the angle between the longitudinal axes of the grooves is less than 90xc2x0. This makes the shearing effect of the grooves extremely good, and the apparatus has an extremely good melting, grinding and mixing performance. The idea of a third preferred embodiment is that the pitch angles of either of the grooves are arranged to be about 90xc2x0, whereby the yield of the apparatus is extremely good. It is the idea of a fourth preferred embodiment that the rotor and stator grooves are oblique in the same direction, but their pitch angles are arranged different, whereby the grooves having a wider pitch angle determine the direction of the net flow, and in the grooves having a more low-gradient pitch angle, the material flows backward. This makes the dwell time of the material in the apparatus longer and thus the material can be treated more efficiently. However, the angle between the longitudinal axes of the grooves is so sharp that the melting and mixing performance of the apparatus is extremely good. It is the idea of a fifth preferred embodiment that the cross-section of the grooves is flat in the longitudinal direction. This way the grooves are quite spacious for the flow of mass, rendering the yield of the apparatus good.